zmanabba

I have a problem that I have never run into before. 1993 Grand Cherokee 5.2. It's my sons vehicle and I had to tow him to my place when it died from only reading 9 volts at the dash gauge. Replaced alternator, ECU and battery with a known good used battery. After replacing Alternator with a rebuilt unit (NAPA brand) still read 9 volts. Replaced ECU with rebuilt one (CARDONE brand) still read 9volts. Installed different battery read 12 volts. Checked voltage at battery with multi meter and reads 12.1 volts. This is the highest reading that I have gotten. When I checked with the multi meter before the highest reading that I got was around 10. So I know that the the ECU and the battery were bad for sure. I had checked the system with the new alternator and used battery-10 volts. When I changed the ECU I reinstalled his original battery after putting it on a trickle charger for two days and had an initial 13.1 volts per my multi meter. But it wouldn't accept a charge after the ECU replacement so I went back to the other battery. When I check the out put of the alternator with multi meter I get a reading of 25 volts. I have gotten this reading since replacing the alternator. I didn't think to check the original and it's since been turned in for the core charge. I know that the system should be putting out 13.5 to 14.0 volts. I did a search but could not find anyone else who has run into this problem. We do plan on replacing the battery with a new one because I want mine back lol. I don't think that the battery is the problem but I'm open to suggestions

zmanabba

Well with 105 views and no replies, it looks like I'm on my own. When I find the problem I'll post back here with the solution to add to the knowledge base.

warrpath4x4

if your alternator is putting out 25 volts you have the wrong alternator, or you are not reading the multimeter correctly.

as to your original problem, it sounds like your battery cables are suspect if your alternator is new and your battery is still at 9 or 10 volts.

zmanabba

I suspect battery cables also and new ones are on order. It's my son's car and I only have access to it when he isn't working so I work on it when I can. I also work for Fedex and we're a little busy this time of year lol. The alternator is correct, checked the part number several times. I take no offence that you are making sure that I'm reading the multi meter correctly but I've been working on cars since I was 11 (now 58). I even worked as a mechanic back in the 80's but found that I much prefer it as a hobby. I asked because I know that every vehicle has it's quirks and I was hoping that this was one of them and I could be quickly pointed to the problem. I feel that the alternator is trying to overcome resistance in the electrical system and that's why it was maxed out at 25 volts. I bear no hard feelings at the lack of response unfortunately text doesn't always convey that. I will keep everyone updated so that if someone else runs in to the same problem they won't have to go through the same problem. Thank you

wingless

This topic shows my generator tests, per the FSM.

Charlie Dog

Have you checked to see the wire from alternator to battery is not broken?

zmanabba

Problem solved! I want to thank all of you for your suggestions. It always helps to have another set of eyes on the problem. Today my son and I both had the same day off. It helps immensely to be able to work on things in the day light and not doing an 11 hour shift and trying to trouble shoot. So after cleaning all grounds and replacing the cable ends with some higher quality cable ends. I don't know how to post a link but I got them off of Amazon for about 20 dollars if you want to do a search. After all of that the system is still showing 12.3 volts to the battery. I had previously checked the fuses with my trouble light and they all checked good. This time I went through with my Volt meter. The Alt fuse closest to the engine (60 Amp) checked 25 volts on one side and 12.3 on the other hmm. So I pulled it and it was cloudy so I couldn't see all of it but the plastic wasn't burnt. Checked it with the Ohm meter and was open. Put in a new fuse and the system now shows 14 volts per the dash gauge. My guess is the system was back feeding and that is why the fuse was getting power to both sides. If someone were to hold a gun to my head I would say that the root cause was the bad battery connections causing the system to spike. The alternator and the computer were bad since the voltage would go up with each replacement of them but I feel that the bad post connections caused it. I hope that this might save someone else a headache weeks, months or years from now. Oh and I will be replacing the battery cables at a later date. I have zero desire to do it now with my present work load and needing to lay on my back in the snow lol.

warrpath4x4

glad you got it fixed and that you responded to let everyone know.

on battery cables I build my own out of #2 welding ground cable, and its the kids jeep so make him lay in the snow lol.